(પ.ક્ર.: $Mn\, = 25, Co\, = 27, Ni\, = 28, Zn\, = 30$)
In all these complexes, the central metal ion is in $+2$ oxidation state.
$Zn^{2+}$ has $3d^{10}$ outer electronic configuration with $0$ unpaired electron.
$Ni^{2+}$ has $3d^8$ outer electronic configuration with $2$ unpaired electrons.
$Co^{2+}$ has $3d^7$ outer electronic configuration with $3$ unpaired electrons.
$Mn^{2+}$ has $3d^5$ outer electronic configuration with $5$ unpaired electrons.
Hence the correct order of spin - only magnetic moments is
${[MnC{l_4}]^{2 - }}\, > \,{[CoC{l_4}]^{2 - }}\, > \,{[NiC{l_4}]^{2 - }}\, > \,{[ZnC{l_4}]^{2 - }}$
$(i)$ $\left[ M ( NCS )_{6}\right]^{(-6+ n )}$
$(ii)$ $\left[ MF _{6}\right]^{(-6+ n )}$
$(iii)$ $\left[ M \left( NH _{3}\right)_{6}\right]^{ n ^{+}}$